Argon (Ar) – element 18
Argon is a chemical element with the symbol Ar and atomic number 18. It is a noble gas in group 18 (noble gases), period 3 of the periodic table (p-block), and is a gas at room temperature.
Argon (Ar) has atomic number 18, atomic mass 39.948 u and electron configuration [Ne] 3s2 3p6.
Argon facts
| Symbol | Ar |
|---|---|
| Atomic number | 18 |
| Atomic mass | 39.948 u (g/mol) |
| Category | noble gas |
| Group | group 18 (noble gases) |
| Period | 3 |
| Block | p-block |
| Phase at 20 °C | Gas |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 |
| Noble-gas notation | [Ne] 3s2 3p6 |
| Electrons per shell | 2, 8, 8 |
| Valence electrons | 8 |
Bohr model and shells
Argon has 18 electrons in 3 shells: 2, 8, 8. Full configuration and noble-gas notation are in the table; work out any element or ion with the electron configuration calculator.
Physical and atomic properties
| Melting point | 83.81 K (-189.3 °C) |
|---|---|
| Boiling point | 87.302 K (-185.8 °C) |
| Density | 1.784 g/L |
| Electron affinity | -96 kJ/mol |
| Ionization energies | 1520.6, 2665.8, 3931 kJ/mol (1st, 2nd, 3rd) |
| Discovered by | Lord Rayleigh |
Use the atomic mass in the molar mass calculator for any formula containing Ar.
Position in the periodic table
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Frequently asked questions
What is the atomic mass of argon?
The atomic mass of argon is 39.948 u, so one mole of argon atoms weighs 39.948 g.
What is the electron configuration of argon?
Argon has 18 electrons: 1s² 2s² 2p⁶ 3s² 3p⁶, or [Ne] 3s² 3p⁶ in noble-gas notation. Electrons per shell: 2, 8, 8.
How many valence electrons does argon have?
Argon has 8 valence electrons (group 18).
Is argon a metal?
No. Argon is a nonmetal (noble gas).
Where is argon on the periodic table?
Argon is in group 18 (noble gases), period 3, in the p-block.
Data: Periodic-Table-JSON (CC BY-SA 3.0); standard atomic weights from IUPAC (abridged). Values in brackets are the mass number of the longest-lived isotope.